[Boatanchors] "Sweep" techniques

Fri Jan 7 22:42:25 EST 2011

HP and Tek FET probes are fine, but you still have to be careful because
they have a few pF to Ground which can detune things.

-John

==============

> I forgot to mention the HP FET probe. - Al
>
> On 1/7/2011 10:16 PM, J. Forster wrote:
>> Use a DC Block or you'll wipe out the SA input mixer!!! You should
>> probably also use an attenuator/matching pad.
>>
>> -John
>>
>> ==================
>>
>>
>>
>>> The Tektronix 7000 series scopes I use provide a buffered
>>> output from the selected vertical amp, I often use this to feed a
>>> frequency counter.  I imagine you could also use this output to feed a
>>> spectrum analyzer so the circuit loading would be that of the vertical
>>> plug-in and probe (either 1 or 10 meg).  I wouldn't try to use this
>>> technique at VHF/UHF or with pulse waveforms but it should be fine for
>>> looking at fairly low frequency IF strips and filters.
>>>
>>> Rodger WQ9E
>>>
>>> ----------------------------------------
>>> From: "Carl"<km1h at jeremy.mv.com>
>>> Sent: Friday, January 07, 2011 9:00 PM
>>> To: "Al Klase"<al at ar88.net>,<boatanchors at mailman.qth.net>
>>> Subject: Re: [Boatanchors] "Sweep" techniques
>>>
>>> The problem with an SA is that its 50 Ohms and would seriously load
>>> down
>>> an
>>> IF strip or xtal filter.A sweeper and storage scope is more realistic
>>> since
>>> the sweeper is designed for the job and the scope wont load down the
>>> circuit.
>>>
>>> Johns explanation was the way I first did it, in the early 60's.
>>> Tedious
>>> but
>>> thats how everything was then.
>>>
>>> For a good description of the old way see the WW2 Super Pro manual. It
>>> also
>>> covers IF alignment without the test equipment and IMO its mandatory
>>> reading
>>> before doing any of the early HQ series. IMHO I can do a better job
>>> faster
>>> with a sig gen, meter and ear on a HQ.
>>>
>>> Another good read is the HRO-60 manual.
>>>
>>> Many users want to either narrow or widen the factory selectivity if
>>> they
>>> are dedicated CW or AM operators. This can be done by peaking, stagger
>>> tuning, loading or unloading the IF circuit with a resistor (increasing
>>> or
>>> removing the transformer swamping resistor for some Collins for AM),
>>> regeneration, and more. Not all are very good or limit the sets
>>> usefulness.
>>> These days its easier to add a Kiwa AM filter than try to custom tune
>>> the
>>> IF's.
>>>
>>> To keep in the BA spirit I use a GR-1025A sweeper which still has the
>>> National Radio inventory tag. The scope is a lot more modern. I also
>>> have
>>> several HP items for when the spirit or the job moves me.
>>>
>>> Carl
>>> KM1H
>>>
>>> ----- Original Message -----
>>> From: "Al Klase"
>>> To:
>>> Sent: Friday, January 07, 2011 4:06 PM
>>> Subject: Re: [Boatanchors] "Sweep" techniques
>>>
>>>
>>>> Ron,
>>>>
>>>> A couple of observations from a non-expert:
>>>>
>>>> Sweeping TV and FM IF's is relative easy because their bandwidths are
>>>> wide, 100 of KHz or more.  The primary problem with sweeping the
>>>> narrow
>>>> IF's in communications equipment is that the sweep rate has to be
>>>> drastically reduced to accurately represent the shape of the filter.
>>>> We're probably talking 100's of milliseconds if not whole seconds.
>>>> So,
>>>> you either need a storage scope or a vivid imagination to actually see
>>>> what going on.
>>>>
>>>> The classic test equipment for doing this is a "spectrum analyzer"
>>>> with
>>>> a "tracking generator."  I use an HP 141T (8556A and 8552B plugins)
>>>> with
>>>> an 8443A TG.  The 141T is equipped with a storage CRT.  More modern
>>>> equipment uses digital storage, and is capable of printing out the
>>>> results.  The other advantage of this sort of a spectrum analyzer is
>>>> that it offers 2dB-per-division and 10dB-per-division vertical
>>>> response
>>>> in addition to the linear response available in the usual
>>>> oscilloscope.
>>>> The 10dB/div gives you pictures like you see in the text books,
>>>> allowing
>>>> you to reckon things like the 6/60dB shape factor of a filter.
>>>>
>>>> Hope that helps a little,
>>>> Al
>>>>
>>>> On 1/7/2011 3:09 PM, bonddaleena at aol.com wrote:
>>>>
>>>>>
>>>>> Hello to all. I've been a ham for a long time and there is one area
>>>>> where
>>>>> not only is my knowledge severely lacking, but I seem to be unable to
>>>>> find any decent info on this technique.
>>>>>
>>>>> The subject is 'sweep alignment' of IFs and filters, etc.
>>>>> I have quite a few Tek 'scopes, and also a nice collection of MODERN
>>>>> Sweep/Function Generators. Krohn-Hite, Exact, etc. I have also
>>>>> purchased
>>>>> and repaired a ton of test equipment including 'scopes and TDRs, in
>>>>> addition to my boatanchor collection.
>>>>> The manuals for the Sweepers assume you know how to connect them and
>>>>> use
>>>>> them.
>>>>>
>>>>> A while back, I noticed that there were several articles in ER
>>>>> Magazine
>>>>> showing the swept response of various boatanchors, (SX-117, etc).
>>>>> Unfortunately, the authors never describe the test methodology. I
>>>>> have
>>>>> purchased more than a few (!!) "How to use your Sweep/Signal
>>>>> Generator"
>>>>> books.
>>>>> However, they are pretty old and only deal with old, tube type TVs.
>>>>> I even suggested to Ray at ER Mag that this subject would make a
>>>>> great
>>>>> article and he agreed, but I still haven't seen anything.
>>>>>
>>>>> So, could some of you guys with all the expertise in this area (Carl,
>>>>> Al)
>>>>> at least give me a shove in the right direction?
>>>>>
>>>>> Yes, I have searched the WWW extensively and no joy......
>>>>>
>>>>> Thank you!
>>>>>
>>>>> ron
>>>>> N4UE
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>>
>>
>